Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1–2
Observers in the Southern Wallowas have noticed a layer of buried surface hoar that has been mostly found at mid elevation bands on NW-NE aspects and produced natural avalanches following the foot of new snow that fell on 12/16-12/17. Check out the pro observation from this time period here. The solstice rain event started out as snow at the Schneider Meadows Snotel (5400'), and between the evening of 12/19 and the evening of 12/20, this station recorded 9" of new snow before likely turning to rain with a total snow water equivelant of 2". Forecasters have not verified, but expect there to have been a widespread natural avalanche cycle during this event. If you have any observations from this time, (or any time!) please submit information and/or pictures to the WAC here. Just as the name suggests, persistent weak layers are persistent and take time (often on the scale of weeks), to stabilize. Patience is required by the any backcountry traveller when dealing with a persistent slab avalanche problem. I would expect this persistent slab to be reactive to a person and/or machine in the right spot. Careful snowpack assessment and patience are necessary as these persistent weak layers could be more easily triggered where the solstice rain crust is thinner. Where might this crust be thinner? I would expect it to be thinner at higher elevations wherever the freezing line was. When uncertainty in the the snowpack exists, create a margin for yourself by choosing simple terrain void of terrain traps and stick to lower angle slopes (less than 35 degrees). Look for red flags of instability such as shooting cracks, whumphing, and recent avalanche activity- if seeing any of these signs, choose lower angle and more simple terrain.
